Sen. Dianne Feinstein acknowledged on Capitol Hill the tough road ahead for the gun legislation she introduced on Thursday despite the shock and grief over last month’s school shooting in Newtown, Conn.

WASHINGTON — During a lengthy and at times emotionally wrenching news conference, Sen. Dianne Feinstein on Thursday announced legislation that would ban the sale and manufacture of 157 types of semiautomatic weapons and magazines holding more than 10 rounds of ammunition.

The bill, which Ms. Feinstein (D., Calif.) introduced in the Senate on Thursday, would exempt firearms used for hunting and would grandfather in certain guns and magazines. The bill’s goal, she said, would be “to dry up the supply of these weapons over time.”

Ms. Feinstein, surrounded by victims of gun violence, congressional colleagues, and law enforcement officials, stood near pegboards with 10 guns attached as she admitted the difficulty in pursuing such legislation, even when harnessing the grief over the shooting of 20 schoolchildren in Newtown, Conn., last month.

“This is really an uphill road,” she said.

Since the expiration of a ban on assault weapons in 2004, lawmakers have shown a deep reluctance to revisit the issue. They cite a lack of evidence that the ban was effective and a fear of the gun lobby, which has made inroads at state and federal levels in increasing gun rights over the past decade.

Many lawmakers, including some Democrats, prefer more modest measures to curb gun violence, such as a bill that would enhance background checks of gun buyers or focus on enforcement of existing laws.

One such measure has been introduced by Sen. Patrick Leahy (D., Vt.), chairman of the Senate Judiciary Committee, who will start hearings next week on gun violence. His bill would give law enforcement officials more tools to investigate so-called straw purchasing of guns, in which an individual buys a firearm for someone who is barred from obtaining one on his own. Among the witnesses will be Wayne LaPierre, the executive vice president of the National Rifle Association.

“Sen. Feinstein has been trying to ban guns from law-abiding citizens for decades,” said Andrew Arulanandam, a spokesman for Mr. LaPierre. “It’s disappointing but not surprising that she is once again focused on curtailing the Constitution instead of prosecuting criminals or fixing our broken mental health system.”

More legislation is expected to arise soon. Sen. Kirsten Gillibrand (D., N.Y.) and Sen. Mark Kirk (R., Ill.) have agreed to work on gun-trafficking legislation; no federal law defines gun trafficking as a crime. Mr. Kirk is also working on a background-check proposal with Sen. Joe Manchin III, (D., W.Va.), a Democrat with a strong gun-rights record.

Joining Ms. Feinstein on Thursday were Rep. Carolyn McCarthy (D., N.Y.), who will introduce companion legislation in the House, and Sen. Richard Blumenthal (D., Conn.), who talked about the Newtown shooting.

“I will never forget the sight and the sounds of parents that day,” he said.

Several gun-violence victims, families of those killed, and others gave brief statements in favor of the bill.

The bill — which, unlike the 1994 assault weapons ban, of which Ms. Feinstein was a chief sponsor, would not expire after it is enacted — would ban certain characteristics of guns that make them more lethal and would require that grandfathered weapons be registered. More than 900 guns would be exempt for hunting and sporting.

Many Republican lawmakers, the NRA, and some Democrats oppose such a measure. “I don’t think you should have restrictions on clips,” Sen. Tom Coburn (R., Okla.) said. “The Second Amendment wasn’t written so you can go hunting; it was to create a force to balance a tyrannical force here.”

Backers of the ban say that the 1994 measure helped curb gun violence.

“The original bill, though flawed, had a definite impact on the number of these weapons faced by the police on streets and used in crimes,” said Adam Eisgrau, who helped write the ban. He said the new bill, with more explicit language on the types of features on banned weapons, “is far more respectful of firearms for recreation uses.”

Bans on assault weapons and high-capacity magazines were among the proposals made by President Obama and Vice President Joe Biden last week. Mr. Biden took the campaign for tougher gun laws to the Internet on Thursday in an online video chat as an effort by the White House to build public support.